# The winter weather products

> What the Winter Storm Severity Index, the winter precipitation probabilities and the Day 3 to 7 hazards each measure.

Developers · Concept · https://wxalerts.org/docs/developers/concepts/winter-products/

The routes and fields are on the [winter weather reference](/docs/api/winter/).

- **WSSI, the Winter Storm Severity Index.** WPC's forecast of how much
  disruption winter weather may cause, not how much falls: the same 6 inches
  of snow rates higher where it rarely snows. It comes as an overall category
  plus the components behind it, for three 24 hour days. The published
  components are `snow_amount`, `snow_load` (weight of snow on trees and power
  lines), `ice_accumulation` and `blowing_snow`.

- **PWPF, the Probabilistic Winter Precipitation Forecast.** WPC's chance
  that a 24 hour period brings at least a given amount: 4, 8 or 12 inches of
  snow, or 0.01, 0.10 or 0.25 inch of freezing rain accretion ("ice" here
  means freezing rain, which is what the product measures).

- **Day 3 to 7 hazards, winter only.** WPC's medium range hazards outlook,
  keeping only `heavy_snow`, `freezing_rain` and `hazardous_cold`. It is a
  set of labelled areas with dates; WPC attaches no probability to it.